1. Field of the Invention
This invention relates to the manufacture of titanium dioxide nanopowder. More particularly, the invention relates to the manufacture of titanium dioxide nanopowder of controlled particle size in a gas phase flame reactor by using a cesium substance.
2. Background of the Invention
The scientific and technological advantages of nanostructured particles and materials have been attracting considerable attention. The small size of nanoparticles (generally used to indicate particles less than 100 nm in diameter), which can be responsible for different useful properties (electronic, optical, electrical, magnetic, chemical, and mechanical), makes them suitable for a wide variety of industrial applications.
The manufacture of pigmentary titanium dioxide by oxidizing titanium tetrachloride in the gas phase in a flame reactor with an oxygen-containing gas is known. U.S. Pat. No. 5,201,949 describes the addition of cesium chloride for purposes of improving carbon black undertone, specific surface area and gloss properties.
Producing titanium dioxide nanopowder in a commercial scale flame reactor poses significant challenges. Identifying the appropriate operating conditions that can produce acceptable nanopowder product without causing reactor pluggage can be a significant a problem. Also operating conditions considered useful for producing titanium dioxide nanopowder can be difficult to carry out in a flame reactor due to aforementioned concerns with reactor pluggage and to related operating parameters that lead to the formation of particles and aggregates of particles of a size larger than that desired for typical nanoparticle applications. Deliberate control of a flame reactor in a manner that promotes the preferential generation of nanoparticulate materials is made difficult due to a propensity of impacts between particles at high pressures and mass loadings, leading to aggregate formation and particle growth. This can also lead to excessive wall deposition, resulting in the constriction of flow and ultimately to downstream pluggage of the reactor system.